The Mediterranean fruit fly (Medfly, Ceratitis capitata), is possibly the most important agricultural pest of fruits and vegetables in temperate and subtropical regions. Being a qualitative pest, its status is not based on fruit biomass damaged, but rather on presence or absence of eggs or larvae.
The Sterile Insect Technique (SIT) is the accepted alternative for selective regional control of C. capitata. Examples of other insects that are successfully controlled using SIT or which are the targets for the development of such methods are Screwworm fly, Anopheles mosquito, Tsetse fly (Glossina spp), Painted Apple Moth (Lep: Lymantriidae) and Aedes mosquitoes.
Briefly, SIT is based on mass-production and release of irradiated sterile males, intended to compete numerically and qualitatively with feral fertile males by preventing the deposition of fertile eggs. SIT has been applied successfully to eradicate or reduce pest populations below a critical threshold of economic damage. The current protocol for C. capitata control is to release irradiated sterile males twice-weekly, throughout the year, in order to preclude subsequent possible mating with wild-type fertile males and prevent deposition of fertile eggs. There are several problems associated with the current practice: Firstly, irradiated males are less viable in the field and do not survive for as long as do feral males. Secondly, many of these facility-reared irradiated males mate for shorter periods and transfer less sperm to the female, and in consequence, such females subsequently re-mate sooner than those that have previously mated with feral males. Thirdly, under normal circumstances, unmated females, or females that have mated with irradiated (sterile) males, produce infertile eggs at a reduced rate, but their deposition in fruit is not in accord with the quarantine regulations of zero tolerance of infestation demanded.
WO 01/039599 discloses a new approach to SIT in which male insects homozygous for a dominant lethal gene are released and mate with wild insects thus producing progeny that are heterozygous for this dominant lethal gene and therefore invariably die.
Male-derived accessory gland proteins (Acps) are transferred to the female reproductive tract during mating and affect a variety of functions in the virgin female recipient involved in female reproductive maturation, behavior and fitness (reviewed in e.g. Wolfner, 2007). Most of the basic and physiological studies of the involvements of Acps in the post-mated female have been performed On the fruitfiy, Drosophila melanogaster. Several Acps have been disclosed in e.g. U.S. Pat. Nos. 6,955,897 6,380,159, one of which is an accessory gland protein which is toxic to insect cells and can be used to kill or inhibit the development of insects. The first and most thoroughly studied of the Acps to date is the D. melanogaster Sex Peptide (Acp70A, DrmSP) (see review by Wolfner et al., 2005). The gene encoding DrmSP has been cloned and sequenced (Styger, 1992). It is a single copy gene containing one intron, coding for a 55 amino acid peptide (FIG. 1). Secretion from the main cells of the accessory glands involves its release from the N-terminal signal peptide of 19 amino acids. Mature DrmSP is a linear, unblocked peptide of 36 amino acids, which contains two cysteines forming an S-S bridge. It bears several bioactive domains: a C-terminus regulating female post-mating non-receptivity (Schmidt et al., 1993), an N-terminus priming the functional maturation of the female corpus allatum (CA), resulting in up-regulation of the production of the major female gonadotropin—Juvenile Hormone (JH) (Moshitzlcy et al., 1996) and initiating a cascade of vitellogenesis, oogenesis and egg deposition in the mated female (Soller et al., 1997). Between these two termini, an internal sequence is proposed to up-regulate the humoral innate immunity of the post-mated female (Domanitskaya et al., 2007).
Soon after transfer of the seminal fluid to the female reproductive system, some Acps, including DrmSP, subsequently enter the female hemolymph (Pilpel et al., 2008). Initial activity of that part of the DrmSP molecule that is initially transferred intact into the female hemolymph presumably induces the combined physiological and behavioral responses of the mated female, which are significant but of short duration. Most of the DrmSP molecules bind to sperm via their N-termini and are stored in the female storage organs. From there, they are slowly released over time as truncated DrmSP lacking the N-terminus (hereafter T-SP) and are subsequently transferred to the hemolymph as such, thereby prolonging female post-mating non-receptivity. Allatal maturation and egg development are regulated maximally at this time by allatotrophins and allatostatins. The slow-release from stored sperm is the basis of the extended period of non-receptivity, termed the “sperm effect” (Peng et al., 2005).